1. Field of the Invention
The present patent application for industrial invention relates to an inertial electroacoustic transducer unit.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
As it is known, a traditional loudspeaker comprises a membrane connected to a voice coil that moves in an air gap generated by a fixed magnetic unit. The vibration of the membrane generates a sound.
JP S60 25910 discloses a traditional loudspeaker comprising a membrane connected to a single cylindrical support. A first coil and a second coil are mounted at the ends of the single cylindrical support. Two magnetic units generate corresponding air gaps for the two coils.
Each magnetic unit is of conventional type and comprises a polar core, a toroidal magnet and a polar plate. A magnetic fluid is disposed in the air gap of each magnetic unit in such manner to center the cylindrical support of the coils. Therefore such a loudspeaker does not provide for any elastic suspension that centers the cylindrical support of the coils with respect to the magnetic units.
The magnetic units are locked in position and the cylindrical support of the coils can vibrate in such manner to cause the vibration of the membrane fixed to the cylindrical support.
Recently, inertial electroacoustic transducers, which are commonly known as exciters or shakers, have become popular as an alternative to traditional membrane loudspeakers.
The exciter comprises a coil fixed to a flange intended to be fixed to a rigid element. A centering device supports a magnetic unit in such manner that the magnetic unit generates an air gap wherein the coil is positioned and the magnetic unit can move with respect to the coil. Consequently, vibrations are propagated in the rigid element fixed to the flange of the exciter generating a sound.
Therefore, the inertial electroacoustic transducer is based on a completely different operating principle with respect to a traditional loudspeaker. The exciter is configured in such manner that the magnetic unit moves, while the cylindrical support of the coil remains still. Instead, the traditional loudspeaker is configured in such manner that the cylindrical support of the coil moves, while the magnetic unit remains still. Therefore, an expert of the field who intends to make an inertial electroacoustic transducer would not take a traditional loudspeaker into consideration.
WO2011/029768 in the name of the same applicant discloses an exciter. FIG. 1 shows an exciter according to WO2011/029768, which is generally indicated with reference numeral (100).
The exciter (100) comprises a coil (1) mounted on a cylindrical support (10). The cylindrical support (10) is fixed to a flange (2). The flange (2) comprises a central collar (20) to which the cylindrical support (10) of the coil is fixed. The flange (2) is intended to be fixed to a rigid element (not shown in FIG. 1), such as for example a panel of rigid material, which will be put in vibration to generate a sound.
The flange (2) is connected to a centering device (3) comprising an elastic suspension that supports a magnetic unit (4). The magnetic unit (4) comprises a cup (40) with a base (41) and a lateral wall (42) with a border (46) that define a cylindrical housing wherein a magnet (43) and a polar plate (44) are disposed.
The magnet (43) has a cylindrical shape and is centrally disposed inside the seat of the cup (40) and fixed to the base (41) of the cup (40). The polar plate (44) has a cylindrical shape and is fixed to the magnet (43). The polar plate (44) has a free surface (45) flush with the border (46) of the lateral wall of the cup.
The magnet (43) and the polar plate (44) have a lower diameter than the seat of the cup (40). Consequently, an air gap (T) with toroidal shape is generated between the external lateral surface of the magnet (43) and of the polar plate (44) and the internal lateral surface of the lateral wall (41) of the cup.
The magnetic unit (4) is held by the centering device (3) in such manner that the coil (1) is disposed in the air gap (T).
The centering device (3) comprises an external cylinder (30) fixed to the flange (2) and an internal cylinder (31) fixed to the cup (40). The external cylinder (30) is higher than the internal cylinder (31). The external cylinder (30) of the centering device is connected to the internal cylinder (31) by means of elastically flexible spokes (32) in such manner that the internal cylinder (31) is disposed in concentric position inside the external cylinder (30). In view of the above, the magnetic unit (4) can move in axial direction with respect to the cylindrical support (10) of the coil, along an axis (A) that coincides with the axis of the cylindrical support of the coil.
This type of exciter is impaired by some drawbacks in terms of harmonic distortion.
As it is known, the aforementioned magnetic circuit, which is commonly used in inertial electroacoustic transducers, does not provide a constant magnetic induction field in the air gap and in proximity of regions outside the air gap.
In order to explain this situation, let's consider a hypothetical cylindrical surface, for example a region of the cylindrical support (10), with height equal to 2 times the height of the polar plate (44), symmetrically positioned in axial direction with respect to the height of the polar plate (44), in such manner that said cylindrical surface projects by the same length from the planar, upper and lower surfaces (45) of the polar plate (44).
The radial lines of the magnetic field, which perpendicularly intersect said cylindrical surface and are the useful components for the movement of the magnetic unit with respect to the coil, are not generally uniform and constant in the two cylindrical surface regions that exceed the height of the polar plate (44). This is caused by geometrical arrangement of the magnetic system and can be assessed both with instruments and software simulation systems.
When the magnetic unit (4) is moved upwards in the direction of the arrow (F1), the magnetic unit gets away from the coil (1). On the contrary, when the magnetic unit (4) is moved downwards in the direction of the arrow (F2), the magnetic unit gets closer to the coil (1). These movements affect the aforementioned cylindrical surface regions that protrude from the border (46) of the polar plate (44), where the lines of the magnetic field are not constant, generating distortions in the production of mechanical vibrations and in the reproduction of sounds. Consequently, a harmonic distortion occurs.
The Total Harmonic Distortion (THD) is a measuring unit that measures total harmonic distortion, which must be taken in great consideration when assessing the quality of an audio device that needs to reproduce an audio program with high fidelity.
The purpose of the present invention is to eliminate the drawbacks of the prior art by disclosing an inertial electroacoustic transducer unit provided with low harmonic distortion.
Another purpose of the present invention is to disclose such an inertial electroacoustic transducer unit that is capable of managing high-power audio signals with reduced radial dimensions.